The use of implantable prosthetic joints to replace natural joints in humans and in animals is an established theraputic procedure. Many designs for such prosthetic joints are known.
One example of an implantable prosthetic joint design is found in U.S. Pat. No. 4,470,158, issued Sept. 11, 1984, to Pappas et al. The prosthetic joint of Pappas et al includes a first component for attachment to a first bone, a second component for attachment to a second bone and a bearing component therebetween. There is substantially congruent engagement between the components.
Pappas et al discloses an articular surface on the second component and a corresponding congruent articular surface on the bearing component which surfaces are generated by rotating a common generating curve around a plurality of predetermined generating axes to create multicentric surfaces. The purpose of the multicentric congruent surfaces of Pappas et al is to provide a free floating or unconstrained relative motion between the bearing surface and the second component surface while discouraging extrusion of the bearing component.
Another example of a prosthetic joint can be found in U.S. Pat. No. 4,085,466, issued Apr. 25, 1978, to Goodfellow et al.
Prosthetic joints such as those identified in the above mentioned patents have enjoyed commercial success. However, in prosthetic joint designs which provide free floating contact between the bearing component and both other components, extrusion of the bearing has remained a problem in patients having weark or damaged ligaments which are not strong enough to hold the bearing component in place between the other components. There has existed a need for a prosthetic joint which provides at least some free floating contact between the bearing component and a component to be attached to a bone while at the same time capturing the bearing component so that extrusion of the bearing component is avoided.